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[chemsep05]

I'm designing a facility to handle 100 mol/s of equimolar n-Pentane and Benzene using Sulfolane as the solvent, I need to recover at least 99.98% Benzene with not more thatn 2.5% n-pentane present in the extract, I'm using chemsep for the preliminary design which, is based on equilibrium stage calculations, but I can't seem to get a high enough purity at a resonable temperature, It seems to like temperatures around 230K, How can I increase the purity by other means?

[sgkim]

(1) An extractive distillation system shall be composed of two columnms - extractive distillation column(EDC) and solvent recovery column(SRC). The cold solvent sulfolane shall be fed to top part and BZ-NP mixture to middle part of EDC. The extract(BZ-"rich solution") shall be drawn off from the bottom and fed to the middle part of the SRC.

Benzene shall be drawn from the top of the SRC and sulfolane shall be regnerated as lean solution and recycled to EDC. NP shall be produced as raffinate from the top of EDC.

1) To increase the purity of BZ by decreasing the content of NP, the number of stripping zone trays(lower part of the EDC feed tray) shall be increased.

Once much amount of NP carries over from EDC bottom to SRC, nothing can be done in SRC.

2) To increase the purity of BZ by decreasing the content of sulfolane, the number of rectifying zone trays(upper part of SRC feed tray) shall be increased. Or increase the reflux ratio of SRC. If too much sulfolane content is expected in BZ then increase the number of trays and reflux ratio together.

Residual BZ content in sulfolane(BZ-"lean solution") may not be a problem so far as the BZ quality is concerned. But if the BZ content increase in the "lean sulution" the recovery ratio of BZ will drop.

(2) 230K is equal to -43.2℃ !! I can't imagine what'll be the absolute pressure of SRC.

Stefano/051108